London, Jan. 4: If “jamming” after school is “vanilla”, you could always “tear” for a “za” with your friends.

For most people over the age of 15 — particularly bemused parents struggling to understand the ever-shifting changes in teenage slang — this sentence will mean absolutely nothing.

But now, with an idea that started off as a joke, a 13-year-old girl has written a bestselling dictionary translating such language for the benefit of a bewildered adult generation. Lucy van Amerongen’s The A-Z of Teen Talk was a surprise hit this Christmas, with parents and teenagers snapping up the £4.99 book.

Over the course of a year, the Cheltenham Ladies College student from Box, near Nailsworth, Gloucester, compiled a list of 300 words or phrases and their meaning.

For the uninitiated, if something is “vanilla”, it is boring; “jamming” means hanging around; while to “tear" is to leave quickly, or run away.